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Following decades of research on stress and its impact on behaviour, it is now widely accepted that selective psycho-pathologies, in particular clinical depression are more prevalent in humans with prior history of life-stress events. Interest in stress has led to questions about how it might affect the physiology and behaviour of animals exposed indirectly during gestational development. Not unexpectedly gestational stress has been shown to affect the offspring in several ways: endocrine responses to stress are elevated, fear, arousal and affective disturbances are all subject to vary if the pregnant animal is subjected to periods of aversive stimulation.
Beginning in 1997, Michael Meaney of McGill University produced a series of publications suggesting that peri-natal events influence offspring and infant development, not via physical discomfort or physiological disturbance, but does so through modifications of maternal behaviour. Highly nurturant mothers (those who engage in active arched-back nursing (ABN), and spend more time licking and grooming (L/G) their pups), programme their offspring with improved cognitive abilities, decreased anxiety and fear, and reduced HPA axis hormone secretion. Low-nurturant mothers, who engage in less ABN and less L/G, tend to programme the opposite responses in their offspring. Our initial foray into this field was to investigate if gestational stress might also produce responses in the offspring via changes in maternal behaviour, and indeed ABN and L/G were reduced in dams which were subjected to gestational stress. We queried why stressed Dams would be less maternal towards their infants, and tested gestationally-stressed Dams in the Porsolt test for depressive-like behaviour. Our results suggested that these stressed Dams were actually depressed and this resulted in less maternal behaviour. Human mothers with depression are also less maternal and have been shown to divest themselves of infant care much like our prenatally-stressed Dams. On this basis we have proposed that gestational stress induced decrements in maternal behaviour represent a novel rat model for postnatal depression with face and construct validities.
In the present work we have attempted to replicate the findings of Smythe¿s group (Smith et al., 2004), and have investigated the potential for antidepressants to alter the influence of gestational stress on maternal behaviours and depressive-like response, and whether or not the offspring¿ are modified by maternal treatment with ant-depressants. Approximately 140 time-mated, lister hooded rats were generated in house, and subjected to gestational stress on days 10-20 (1hr restraint/day) or remained undisturbed in their home cages. Following birth, cohorts of control and stressed Dams were administered vehicle or an antidepressant (imipramine 15mg/kg; or sertraline 10mg/kg) once daily until postnatal day 10.
We assessed maternal Porsolt activity, nurturance (ABN, L/G, nest building) and anxiety-like behaviour in the elevated plus maze (EPM). Representative offspring of each Dam¿s treatment conditions were maintained post weaning and assessed in the Porsolt and EPM to determine if any changes in maternal behaviour elicited by the antidepressants altered their behavioural programming. Our findings confirm that Dams show depressive-like symptoms following gestational stress, and that administration of antidepressants to the Dams reduces depressive-like behaviour and increased maternal care.
We propose that rat gestational stress is a putative model for human postnatal depression. Prenatal stress effects on maternal behaviour in the rat Dam represent a novel, and innovative model for human postnatal depression.

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